The MPLS WG Archive

[Shahram Davari <Shahram_Davari@pmc-sierra.com>]

Hi,

A new draft by Bora Akyol and Puneet Agarwal will be published soon that covers this.

-Shahram

> -----Original Message-----
> From: Eric W Gray [mailto:ewgray@mindspring.com]
> Sent: Tuesday, August 21, 2001 1:56 PM
> To: Ray Qiu
> Cc: MultiProtocol Label Switching Mailing List
> Subject: Re: Time to live
> 
> 
> Yes, that has been suggested as a logical extension of the 'Pipe'
> model in DiffServ.  I don't recall where that effort is at right now
> but I don't think the work has been adopted by either the MPLS
> or CCAMP working groups.  Do you know?
> 
> --
> Eric Gray
> 
> Ray Qiu wrote:
> 
> > There is also an option that we don't copy the MPLS TTL 
> back to IP TTL.
> > It makes IP think the MPLS LSP is only one hop.
> >
> > Thanks,
> > Ray
> >
> > On Tue, 21 Aug 2001, Eric W Gray wrote:
> >
> > > Date: Tue, 21 Aug 2001 13:10:17 -0400
> > > From: Eric W Gray <ewgray@mindspring.com>
> > > To: Alexander Marhold <alexander@marhold.at>,
> > >      MultiProtocol Label Switching Mailing List <mpls@UU.NET>
> > > Subject: Re: Time to live
> > >
> > > Below, the last sentence was supposed to be "Note that Frame
> > > Relay ..."
> > >
> > > --
> > > Eric Gray
> > >
> > > Eric W Gray wrote:
> > >
> > > > Alexander,
> > > >
> > > >     No cigar.  The distinction is not cell verses 
> frame, but rather
> > > > whether or not it is possible to incorporate the label in the L2
> > > > encapsulation.  Where this is possible, ATM and FR, there is
> > > > no TTL capability in the L2 encapsulation.  Not that Frame
> > > > Relay is Frame based...
> > > >
> > > > --
> > > > Eric Gray
> > > >
> > > > You wrote:
> > > >
> > > > > Hello
> > > > > I want to explain the mechanism a little bit more in detail
> > > > >
> > > > > FRAME based general:
> > > > > 1. normally at the ingress LSR the IP-TTL is copied 
> into the TTL-field of
> > > > > the label header.
> > > > > 2. the label-TTL is decremented at each hop by 1
> > > > > 3. when it reaches 0 the labelled packet will be dropped and a
> > > > > TTL-exceeded-ICMP message will be sent if possible
> > > > > 4. at the egress the label-TTL is copied back into the IP-TTL
> > > > >
> > > > > CELL based general:
> > > > > 1. normally at the ingress LSR the IP-TTL is copied 
> into the TTL-field of
> > > > > the label header.
> > > > > 1a. the ingress LSR to the ATM-MPLS cloud either 
> decrements the TTL by 1
> > > > > 1b              or by the amount of ATM_MPLS hops of 
> the LSP ( this he knows from the
> > > > > LSP-setup using downstream on demand label allocation 
> and ordered
> > > > > lsp-control label setup)
> > > > > 2. then the packet is chopped into cells
> > > > > 3. the egress reassembles the packet and copies the 
> label ttl back into the
> > > > > IP-TTL
> > > > >
> > > > > if 1a is used then the ATM-MPLS cloud looks like a 
> 1-hop network
> > > > >
> > > > > special features:
> > > > > a) on cisco LSRs there is the possibility to disable 
> the copying of the
> > > > > IP-TTL to the label-TTL and the label-TTL again starts at 255.
> > > > > on the egress the smaller of the 2 TTL-values ( label 
> and IP-header) will be
> > > > > used for the IP-TTL
> > > > > then for traceroute the MPLS cloud looks like a 1-hop 
> (2-hop with PHP)
> > > > > network
> > > > >
> > > > > with best regards
> > > > >
> > > > > Alexander
> > > > >
> > > > > 
> __/__/__/__/__/__/__/__/__/__/__/__/__/__/__/__/__/__/__/__/__/
> > > > >      __/
> > > > >     __/   Dipl.Ing. Alexander Marhold MBA
> > > > >    __/   CCIE #3324, CCNP, CCDP, CCSI #20642
> > > > >   __/   Core & IP Services <Senior Consultant>
> > > > >  __/   Mobile: ++43-(0)664-16 28 234
> > > > > __/   PRO IN http://www.proin.com
> > > > >
> > > > > -----Original Message-----
> > > > > From: owner-mpls@UU.NET [mailto:owner-mpls@UU.NET]On Behalf Of
> > > > > Asim.Khan@vf.vodafone.co.uk
> > > > > Sent: Tuesday, August 21, 2001 6:22 PM
> > > > > To: c-david.escobar@wcom.com
> > > > > Cc: mpls@UU.NET
> > > > > Subject: RE: Time to live
> > > > >
> > > > > It stays the same. The routers only look at the label 
> value not the IP
> > > > > header. When the packet leaves MPLS domain then the 
> normal operation would
> > > > > apply.
> > > > >
> > > > > Asim
> > > > >
> > > > > -----Original Message-----
> > > > > From: David Escobar [mailto:c-david.escobar@wcom.com]
> > > > > Sent: 21 August 2001 17:19
> > > > > To: mpls@UU.NET
> > > > > Subject: Time to live
> > > > >
> > > > > Hi;
> > > > > What happens to the TTL field in the IP header when a 
> labeled packet goes
> > > > > through an LSP? Is it decreased at each router or 
> stay the same?
> > >
>